This invention relates to apparatus and methods for continuously breaking up, removing, and recycling pavement on the roadway. More particularly, this invention relates to a system of recycling the existing pavement on a roadway so as to allow the almost immediate reuse of the resulting multi-gradated aggregate products thereof as a granular subbase over which replacement pavement can be laid. Of course, multi-gradated aggregate products can be put to many uses other than being granular subbase for a section of pavement.
It should be understood that the apparatus and methods described herein could also relate to mobile quarrying applications where the products are stockpiled rather than immediately reused. Rock crushing machines have been used in quarrying operations for some time. Typically, these quarry-based machines have very limited mobility and cannot be efficiently leveled with respect to the terrain. As crushers with greater mobility have been developed, some users have tried to level them by manually adjusting the pressure in the tires supporting the crusher. However, this is time consuming and often impractical when the terrain changes quickly. The crusher can only progress haltingly.
The term multi-gradated aggregate products, as used herein, should be understood to include concrete stone, aggregate, sand, dirt, and other materials found in concrete pavement. The subset of multi-gradated aggregate products which is allowed by specification to be used as subbase under highway pavement is referred to in the art as granular subbase.
Highways, air fields, and many other structures designed for travel are constructed of pavement. Because of its high compressive strength, Portland cement concrete (PCC) is often used in paving. Asphaltic cement concrete (ACC) is also a popular choice. However, the relatively poor tensile strength of these materials often forces designers to specify that reinforcing metallic structures such as steel bars, dowel rods, CD baskets, or mesh extend through the regions of greatest tensile stress. Properly constructed steel reinforced concrete is stronger and less bulky than the nonreinforced variety. On the other hand, many concrete pavements and structures are suitably constructed using little or no steel reinforcement.
Inevitably, time and various forces wear on the structures and even steel reinforced concrete deteriorates, necessitating replacement. Changing public needs often demand the replacement of pavement, regardless of its condition. For example, highways and the like frequently need to be widened or fortified for heavier use.
The composition of a paved roadbed can vary greatly depending on ground conditions and local construction standards. However, a typical pavement surface is comprised of layers. Of course, the upper layer of concrete, PCC or ACC, is most noticeable. The concrete itself is comprised of cement, fine and coarse aggregate, and water. A layer of subbase, such as sand or other fines, is often placed immediately below the concrete. This layer is known as bottom lift. Steel reinforcing bars, dowel rods, CD baskets, or meshes are set in place and become embedded in the concrete as it is poured. These steel structures are known to provide the poured concrete with additional tensile strength. Sometimes the concrete is poured over whatever underlying surface is present, but often a layer of subbase material is placed there first. The subbase material consists of screened or selected multi-gradated aggregate products--usually coarse aggregate, sand, selected fill, asphalt, or concrete. Such a subbase can help spread the load of the concrete slab and provide better drainage thereunder. Underlying the subbase is dirt or other material known as subgrade.
Recently, conservation of natural resources has become a major concern in the construction of concrete highways and the like. Conservation, cost savings, space limitations and regulations have motivated construction companies to search for new ways to reuse existing highway concrete. Landfill regulations in some states and municipalities seriously impinge on contractors' ability to dispose of old concrete which they have removed. Recycling existing concrete highway pavement has been found to reduce costs and save space in the landfills.
Various forms of concrete pavement recycling apparatus and methods exist today. However, they tend to be relatively inefficient, labor intensive, and disruptive of existing traffic. Many conventional methods of pavement recycling require that the broken pavement chunks be transported to a remote site (away from the roadway) for further processing, such as crushing to size and removing and reclaiming the reinforcing steel.
U.S. Pat. No. 5,026,205 to Gorski, issued on Jun. 25, 1991, discloses apparatus and a method for removing, harvesting and recycling pavement. A "train" of equipment is spearheaded by a vehicle having a wedge for prying the concrete up from the ground. While it is suspended, the concrete slab is broken up by blows from two hydraulic hammers pivotally mounted overhead.
This wedge and hammer arrangement breaks up the concrete and jars it loose from the steel reinforcements, but a wedge-accommodating hole in the lane of pavement is required to begin the systematic removal. It takes a great deal of horsepower for this arrangement to plow up the concrete and process it. Since this method is dependent on the train of equipment having good traction on the ground after the concrete has been removed, rainy or muddy conditions can halt or slow the process. Considerable adjustment is also necessary because the size and angle of the wedge must be selected. Furthermore, the angle and pivoting action of the hammers must be adjusted and set.
The Gorski process operates in a rigidly linear fashion to harvest and recycle a single lane of pavement at one time. It is not very flexible. The train of the Gorski reference lacks a trimmer for the simultaneous final grading of the ground to elevation when required. Undesirable fluctuation of the subgrade can result in faults developing later in the concrete.
Furthermore, Gorski fails to disclose efficient means for handling the metallic reinforcing structures (usually steels) that are often present in reinforced concrete pavement. Gorski suggests that a truck 500 can move on the shoulder alongside the crusher to receive any steels discharged. This is impractical if the shoulder is narrow or conditions are muddy. Furthermore, an extra operator is required to drive the truck.
A need exists for apparatus and methods that can, in a single pass and without undue preparation, rapidly, flexibly, and economically remove and recycle an existing lane of pavement. Preferably the system separates the steel and concrete components and renders them into small pieces which are easier to handle and recycle. Ideally, the concrete is rendered into multi-gradated aggregate products. One possible use of these products is to provide a granular subbase which is immediately used as a base for replacement pavement.
Therefore, it is an object of this invention to provide apparatus and methods for continually, rapidly, flexibly and economically breaking up a lane of existing concrete pavement and recycling the same for immediate use in replacement paving.
It is a further and subsequent object of this invention to immediately, rapidly, flexibly, and economically process concrete (and separate the steel when the concrete is steel reinforced) and render the concrete into smaller pieces known as multi-gradated aggregate products which are immediately available for reuse, especially as granular subbase.
It is a further object of this invention to conserve construction materials and avoid waste by recycling existing concrete pavement into material ready for subsequent and even immediate use in repavement.
It is a further object of this invention to provide apparatus and methods whereby the trimming of the subgrade is optionally integrated into the process for recycling concrete into granular subbase and is thereby done simultaneously if desired.
It is a further object of this invention to provide methods which are less likely to be forced to shutdown due to muddy conditions.
It is a further object of this invention to provide apparatus which crushes concrete to coarse aggregate size, removes the steels from the same, trims the subgrade to elevation and places the resulting coarse aggregate on site.
It is a further object of this invention to provide a self-leveling crusher that maintains its crushing means in a level attitude while traversing the roadway.
It is a further object of this invention to provide apparatus and methods which quickly recycles and replaces existing road surfaces.